marine phytoplankton in the presence of toxicants. 

 One of the toxic materials used was lignasan 

 (ethyl mercury phosphate) a bactericide-fungi- 

 cide. She found lignasan to be lethal to all species 

 at 0.06 mg/1 and 0.0006 was the highest level used 

 not causing drastic inhibition of growth. 



Clendenning and North (1960) and North and 

 Clendenning (1958) found that 0.5 mg/1 of mer- 

 cury added as mercuric chloride caused a 50-per- 

 cent inactivation of photosynthesis of the giant 

 kelp, Macrocystis pyrifera, during a 4-day expo- 

 sure. A concentration of 0.1 mg/1 caused a 15- 

 percent decrease in photosynthesis in 1 day and 

 complete inactivation in 4 days. Mercury was more 

 toxic than copper, hexavalent chromium, zinc, 

 nickel, or lead. For phytoplankton, the minimum 

 lethal concentration of mercury salts has been re- 

 ported to range from 0.9 to 60 mg/1 of mercury 

 (Hueper, 1960). The toxic effects of mercury salts 

 are accentuated by the presence of trace amounts 

 of copper (Comer and Sparrow, 1956). 



Lead. — Lead is found as a local pollutant of 

 rivers near mines and from the combustion of 

 leaded gasolines. The lead concentration in sea- 

 water is in the order of 0.00003 mg/1. It is found 

 in marine plants at a level of approximately 8.4 

 mg/1. Residues in marine animals reach a concen- 

 tration in the range of 0.5 mg/1. It is highest in 

 calcareous tissue. 



Wilder (1952) found that lobsters died within 

 20 days when kept in lead-lined tanks, while in 

 steel-lined and other types of tanks, they survived 

 for 60 days or longer. 



North and Clendenning (1958) found that lead 

 was less toxic to the giant kelp, Macrocystis pyri- 

 fera, than mercury, copper, hexavalent chromium, 

 zinc, or nickel. 



Pringle (unpublished data), in studies on the 

 effects of lead on the Eastern oyster, Crassostrea 

 virginica, found a 12-week TLn, value of 0.5 mg/1 

 and an 18-week TL^ value of 0.3 mg/1. Concen- 

 trations of 0.1 to 0.2 mg/1 induced noticeable 

 changes in mande and gonadal tissue under 12 

 weeks of exposure. 



Nickel. — Nickel is found in sea water in a con- 

 centration of about 0.0054 mg/1. Marine plants 

 contain up to 3 mg/1 and this may be higher in 

 plankton. Marine animals contain levels in the 

 range of 0.4025 mg/1. Nickel pollution is caused 

 by industrial smoke and other wastes. It is very 

 toxic to most plants but less so to animals. Haydu 

 (unpublished data), in long-term studies with oys- 

 ters, found that a level of 0.121 mg/1 nickel 

 caused considerable mortality. 



Zinc. — Zinc is found in sea water in a concen- 

 tration of 0.01 mg/1. Marine plants may contain 



up to 150 mg/1 of zinc. Marine animals contain 

 zinc in the range of 6 to 1500 mg/1. It is accumu- 

 lated by some species of coelenterates and mol- 

 lusks. Speer (1928) reports that very small 

 amounts of zinc are dangerous to oysters. 



Clendenning and North (1960) and North and 

 Clendenning (1958) tested the effect of zinc sul- 

 fate on the giant kelp, Macrocystis pyrifera. Four- 

 day exposure to 1.31 mg/1 of zinc showed no ap- 

 preciable effect on the rate of photosynthesis, but 

 10 mg/1 caused a 50-percent inactivation of kelp. 



Other Toxicants 



Ammonia-ammonium compounds. — Ammonia 

 is found in the discharge of many industrial wastes. 

 It has been shown that at a level of 1 .0 mg/1 NH3, 

 the ability of hemoglobin to combine with oxygen 

 is impaired and fish may suffocate. Evidence indi- 

 cates that ammonia exerts a considerable toxic ef- 

 fect on all aquatic life within a range of less than 

 1.0 mg/1 to 25 mg/1, depending on the pH and 

 dissolved oxygen level present. 



Cyanides. — Hydrocyanic acid or hydrogen cya- 

 nide and its salts, the cyanides, are important in- 

 dustrial chemicals. The acid and its salts are 

 extremely poisonous. 



Hydrogen cyanide is largely dissociated at pH 

 levels above 8.2 and its toxicity increases with a 

 decrease in pH. The toxic action of cyanides in- 

 creases rapidly with a rise in temperature. 



Fish can recover from short exposure to con- 

 centrations of less than 1.0 mg/1 (which seems to 

 act as an anaesthetic) when removed to water free 

 of cyanide. They appear to be able to convert cya- 

 nide to thiocyanate, an ion that is not inhibitory 

 on the respiratory enzymes. Complex cyanides 

 formed by the reaction of CN with zinc or cad- 

 mium are much more toxic. However, the reaction 

 between CN and nickel produces a cyanide com- 

 plex less toxic than the CN itself at high pH levels. 



Sulfides. — Sulfides in water are a result of the 

 natural processes of decomposition, sewage, and 

 industrial wastes such as those from oil refineries, 

 tanneries, pulp and paper mills, textile mills, 

 chemical plants, and gas manufacturing facilities. 

 Most toxicity data available are based on fresh 

 water fish. Concentrations in the range of less than 

 1.0 mg/1 to 25.0 mg/1 are lethal in 1 to 3 days. 



Fluorides. — Fluorides are present in varying 

 amounts in the earth's crust. They are used as in- 

 secticides as well as in water treatment and many 

 other uses. While normally not present in industrial 

 wastes, they may be present in trace or higher con- 

 centrations due to spillage. Data in fresh water in- 

 dicate that they are toxic to fish at concentrations 

 higher than 1.5 mg/1. 



Detergents and surfactants. — During the past 



